Linear slide bearing

ABSTRACT

A linear slide bearing for use in, for example, machining center has an integral main body with a channel-like cross-section constituted by left and right skirt portions and a central cavity formed between the skirt portions, the main body having a pair of race receiving grooves formed in the opposing surfaces of the skirt portions confronting the central cavity and non-loaded ball grooves disposed near both ends of respective race-receiving grooves and communicating with the race-receiving grooves. The linear slide bearing further has a pair of bearing races constituted by arcuate members having a semi-circular cross-section, each of said bearing races being provided in its inner surface with a pair of loaded ball grooves.

BACKGROUND OF THE INVENTION

The present invention relates to a linear slide bearing suitable for usein various sliding parts such as the table saddle of a machine tool, theslider of a machining center and the slider of a transportation robotfor reciprocative transportation of a heavy object.

Generally, a conventional linear slide bearing incorporates bearingraces as essential parts thereof. This bearing race, usually made of aflat plate member, is liable to be distorted and twisted when it bears aload, resulting in an unsmoothed recirculation of balls running alongthe bearing race, due to variation of contact pressure between the balland the bearing race along the length of the bearing race. The bearingrace is usually fixed by means of screws. Therefore, a troublesome workis required to fix the bearing race by the screws, particularly when thebearing race has to be fixed at many points. The fixing of the bearingrace by means of screws is disadvantageous in that quite a delicateadjustment of screw tightening force is required in order to correctlylocate and mount the bearing race.

Another problem encountered by the conventional linear slide bearingarises from the difficulty in the formation of non-loaded ball groovesin the main body of the bearing. In the production of the conventionallinear slide bearings, the non-loaded ball grooves are formed in themain body of the bearing by drilling. It is extremely difficult to formthe non-loaded ball grooves in the aimed portions of the main body ofthe bearing directly by drilling. This difficulty not only impairs theprecision of machining but also raises the production cost due to a toolong time required for the drilling.

SUMMARY OF THE INVENTION

Under these recircumstances, the invention aims as its primary object atovercoming the above-described problems of the prior art.

Accordingly, it is an object of the invention to provide a linear slidebearing in which each bearing race is made of an arcuate member having asemi-circular cross-section to exhibit a sufficiently large resistanceto twisting force thereby to ensure a smooth recirculation of the balls.

It is another object of the invention to provide a linear slide bearingin which each bearing race can be mounted easily and precisely simply bybeing fixed at its both ends to corresponding fixing surfaces providedon the inner surfaces of the end covers.

It is still another object of the invention to provide a linear slidebearing which is improved to permit the formation of the non-loaded ballgrooves by a simple grinding, thereby to reduce the production cost ofthe bearing main body and, hence, the production cost of the bearingunit as a whole.

To these ends, according to an aspect of the invention, there isprovided a linear slide bearing comprising: an integral main body with achannel-like cross-section constituted by left and right skirt portionsand a central cavity formed between the skirt portions, the main bodyhaving a pair of race receiving grooves formed in the opposing surfacesof the skirt portions confronting the central cavity and non-loaded ballgrooves disposed near both ends of respective race-receiving grooves andcommunicating with the race-receiving grooves; a pair of bearing racesconstituted by arcuate members having a semi-circular cross-section,each bearing races being provided in its inner surface with a pair ofloaded ball grooves; a track shaft received in the central cavity of themain body and provided at its both shoulder portions with ribs extendingalong the length thereof, the track shaft being provided at the upperand lower sides of each rib with loaded ball grooves corresponding tothe loaded ball grooves in the adjacent bearing race; a pair of endcovers adapted to be attached to both longitudinal ends of the main bodyso as to straddle the track shaft, each of the end cover being providedin its inner surface with ball turning grooves for connecting the loadedball grooves in the bearing races and in the track shaft tocorresponding non-loaded ball grooves in the main body, and raceretaining grooves for retaining adjacent ends of the bearing races; andballs adapted to be recirculated through endless ball passagesconstituted by loaded ball passages formed by the loaded ball grooves inthe bearing races and the track shaft, non-loaded ball passagespresented by the non-loaded ball grooves in the main body and the ballturning grooves formed in respective end covers.

According to another aspect of the invention, there is provided a linearslide bearing comprising: an integral main body with a channel-likecross-section constituted by left and right skirt portions and a centralcavity formed between the skirt portions, the main body having a pair ofrace receiving grooves formed in the opposing surfaces of the skirtportions confronting the central cavity and non-loaded ball groovesdisposed near both ends of respective race-receiving grooves andcommunicating with the race-receiving grooves; a pair of bearing racesconstituted by arcuate members having a semi-circular cross-section,each bearing races being provided in its inner surface with a pair ofloaded ball grooves; a track shaft received in the central cavity of themain body and provided at its both shoulder portions with ribs extendingalong the length thereof, the track shaft being provided at the upperand lower sides of each rib with loaded ball grooves corresponding tothe loaded ball grooves in the adjacent bearing race; a pair of endcovers adapted to be attached to both longitudinal ends of the main bodyso as to straddle the track shaft, each of the end cover being providedin its inner surface with ball turning grooves for connecting the loadedball grooves in the bearing races and in the track shaft tocorresponding non-loaded ball grooves in the main body, and raceretaining grooves for retaining adjacent ends of the bearing races; andballs adapted to be recirculated through endless ball passagesconstituted by loaded ball passages formed by the loaded ball grooves inthe bearing races and the track shaft, non-loaded ball passagespresented by the non-loaded ball grooves in the main body and the ballturning grooves formed in respective end covers; wherein, at each sideof the main body, one of the non-loaded ball grooves and the loaded ballgrooves associated therewith are arranged in symmetry with the other ofthe non-loaded ball grooves and the loaded ball grooves associatedtherewith, with respect to a reference line which coincides with theline of force acting on the track shaft.

According to still another aspect of the invention, there is provided alinear slide bearing comprising: an integral main body with achannel-like cross-section constituted by left and right skirt portionsdepending from a solid portion and a central cavity formed between theskirt portions, the main body having a pair of race receiving groovesformed in the opposing surfaces of the skirt portions and opening to thecentral cavity, and non-loaded ball passages constituted by bores formedin the solid portion of the main body; a pair of bearing racesconstituted by arcuate members having a semi-circular cross-section,each bearing races being provided in its inner surface with a pair ofloaded ball grooves; a track shaft received in the central cavity of themain body and provided at its both shoulder portions with ribs extendingalong the length thereof, the track shaft being provided at the upperand lower sides of each rib with loaded ball grooves corresponding tothe loaded ball grooves in the adjacent bearing race; a pair of endcovers adapted to be attached to both longitudinal ends of the main bodyso as to straddle the track shaft, each of the end cover being providedin its inner surface with ball turning grooves for connecting the loadedball grooves in the bearing races and in the track shaft tocorresponding non-loaded ball grooves in the main body, and raceretaining grooves for retaining adjacent ends of the bearing races; andballs adapted to be recirculated through endless ball passagesconstituted by loaded ball passages formed by the loaded ball grooves inthe bearing races and the track shaft, non-loaded ball passagespresented by the non-loaded ball grooves in the main body and the ballturning grooves formed in respective end covers.

These and other objects, features and advantages of the invention willbecome clear from the following description of the preferred embodimentstaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a linear slide bearing inaccordance with the present invention;

FIG. 2 is a front elevational view of the linear slide bearing with oneof the end covers thereof removed;

FIG. 3 is a sectional view taken along the line III--III of FIG. 2, withthe track shaft thereof being omitted;

FIG. 4 is a sectional side elevational view taken along the line IV--IVof FIG. 2;

FIG. 5 is a front elevational view of the main body of the linear slidebearing;

FIG. 6 is a sectional side elevational view taken along the line VI--VIof FIG. 5;

FIG. 7 is a front elevational view showing a pair of bearing races;

FIG. 8 is a side elevational view of the bearing race as viewed in thedirection of line VIII--VIII;

FIG. 9 is an obliquely cut sectional view of the bearing race takenalong the line IX--IX of FIG. 7;

FIG. 10 is a side elevational view of a track shaft;

FIG. 11 is a front elevational view of the track shaft;

FIG. 12 is an end view of the end cover;

FIG. 13 is a sectional view taken along the line XIII--XIII of FIG. 12;

FIG. 14 is a view showing the inner surface of the end cover;

FIG. 15 is a sectional end view taken along the line XV--XV of FIG. 14;

FIG. 16 is an obliquely cut sectional view taken along the line XVI--XVIof FIG. 14;

FIG. 17 is an obliquely cut sectional view taken along the lineXVII--XVII of FIG. 14;

FIG. 18 is an obliquely cut sectional view taken along the lineXVIII--XVIII of FIG. 14;

FIG. 19 is a side elevational view of a retainer;

FIG. 20 is a front elevational view of the retainer;

FIG. 21 is a cross-sectional view taken along the line XXI--XXI of FIG.19;

FIG. 22 is a front elevational view of another embodiment of the linearslide bearing in accordance with the invention; and

FIG. 23 is a front elevational view of still another embodiment of thelinear slide bearing in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments will be described hereinunder with specificreference to the accompanying drawings.

A linear slide bearing in accordance with the invention has a main bodygenerally designated at a reference numeral 1. The main body 1 is anintegral member having a channel-like cross-section constituted by leftand right skirt portions 3 and 4 opposing to each other and definingtherebetween a substantially rectangular central cavity 2.

As will be best seen from FIG. 5, race-receiving grooves 5 and 6, eachhaving a substantially semi-circular cross-section, are formed in theopposing surfaces of the skirt portions 3 and 4 in symmetry with eachother with respect to the vertical plane containing the longitudinalaxis of the main body 1. Non-loaded ball grooves 7 and 8 having acurvature substantially equal to that of the ball are formed in the mainbody at both sides of the race-receiving groove 5 so as to extend in theaxial direction of the main body 1 over the entire length of the latter.Similarly, non-loaded ball grooves 9 and 10 having a curvaturesubstantially equal to that of the ball are formed at both sides of therace-receiving groove 6. Assuming reference lines Y--Y which intersectthe line X--X of force acting on a later-mentioned track shaft at anangle 30° as shown in FIGS. 2 and 5, the non-loaded grooves 7 to 10 aredisposed on lines Z--Z which intersect the reference lines Y--Y at angleof 60°.

The main body 1 of the bearing is formed from a light-weight materialsuch as a synthetic resin. The light-weight bearing body 1 effectivelydecreases the intertia and, therefore, can suitably be used for thelinear slide bearing which is required to move at a high speed throughrepetitional start and stop.

A pair of bearing races 11 and 12, each being an arcuate member having asemi-circular cross-section, are adapted to be received in therace-receiving grooves 5 and 6 formed in the main body 1. As shown inFIGS. 2 and 7 through 9, loaded ball grooves 13 to 16 corresponding tothe non-loaded ball grooves 7 to 10 are formed in the inner surfaces ofthe bearing races 11 and 12 so as to extend in the axial direction ofthe main body 1. Thus, the loaded ball grooves 13 to 16 are disposed insymmetry with respect to the axis of the main body 1, on theaforementioned lines Z which intersect the reference lines Y--Y at 60°,the reference lines Y--Y themselves intersecting the line X--X of forceacting on the track shaft 18 at 30°. Balls B₁ under the load contact thesurfaces of the corresponding loaded ball grooves 13 to 16 at a contactangle β which is 45° (see FIG. 7). Consequently, the area of contactbetween the surface of each ball and the surface of the associatedloaded ball groove, afforded by elastic deformation of the ball and thegroove, is increased to reduce the level of the load born by the unitarea of the contact region thereby to increase the load capacity of thelinear slide bearing as a whole.

Each of the loaded ball grooves 13 to 16 is constituted by a groovehaving an arcuate cross-section of a radius of curvature which is abouta half of that of the ball. Therefore, each loaded ball can make contactwith the surface of the associated loaded ball groove at two points whenthe ball is preloaded or when it carries a load in any direction so thatit can roll in good manner without making any slip on the surface of theloaded ball groove. Thanks to the contact at two points between theloaded ball groove and the loaded ball, the ball under a heavy load canmake an elastic contact to provide a large contact width to increase therigidity of the linear slide bearing. Since the loaded balls arearranged to roll along four rows of loaded ball grooves in contact withthese grooves at two points at an apropriate angle of contact, the ballsare allowed to make elastic deformation even if there is a slight erroror offset in the mounting plane. Thus, the linear slide bearing of theinvention can absorb slight mounting error or offset to ensure a smoothsliding motion of the main body of the bearing.

The track shaft 18 is received by the central cavity 2 of the main body1 and is fixed to a movable or a stationary part of a machine such as amachine tool by means of bolts or other suitable fixing means. As willbe seen from FIGS. 2, 10 and 11, the track shaft 18 is provided at itsboth shoulders with left and right ribs 18a and 18b. Axially extendingloaded balls grooves 19 to 22 corresponding to the loaded ball grooves13 to 16 in the bearing races 11 and 12 are formed at the upper andlower sides of the ribs 18a and 18b as illustrated. Thus, the loadedball grooves 19 to 22 in the track shaft 18 cooperate with correspondingloaded ball grooves 13 to 16 in the bearing races 11 and 12 in definingfour rows of linear ball passages. As in the case of the loaded ballgrooves 13 to 16 in the bearing races 11 and 12, the loaded ball grooves19 to 22 in the track shaft 18 have an arcuate cross-section of a radiusof curvature which is substantially half of that of the ball. Inaddition, the loaded ball grooves 19 to 22 in the track shaft 18 arearranged to make contact with the loaded balls B₁ at a contact angle β'of 45° to increase the load carrying capacity, as in the case of theloaded ball grooves 19 to 22 in the bearing races 11 and 12.

A plurality of balls B are recirculated through endless ball passagesconstituted by the aforementioned loaded ball passages, non-loaded ballpassages presented by the non-loaded ball grooves in the mainbody 1, andball turning grooves which will be mentioned later. Among these balls,the balls residing in the loaded ball passages will be referred to asthe loaded balls B₁, while the balls in the non-loaded ball passages arereferred to as the non-loaded balls B₂. Thus, each ball can beidentified as a loaded ball when the same is in the loaded ball passageand as a non-loaded ball when the same is in the non-loaded ballpassage.

Reference numerals 23 and 24 designate end covers which are attached toboth longitudinal ends of the main body 1 of the bearing by bolts orother suitable fixing means. The end covers are made from a syntheticresin or a die cast alloy by injection molding or die casting. Sinceboth end covers have an identical construction, the construction of one23 of the end covers will be explained with reference to FIGS. 12 to 18.The end cover 23 is a tabular member having a substantially channel-likecross-section in the plane perpendicular to the axis of the track shaft18. Namely, the end cover 23 has left and right skirt portions 26 and 27defining therebetween a substantially rectangular central cavity 25.Symmetric recesses 28 and 29 are formed in the opposing surfaces of bothskirt portions 26 and 27. The central cavity 25 of the end cover 23,therefore, has a configuration which well approximates that of thecentral cavity 2 of the main body 1 of the bearing. As will be clearlyseen from FIG. 14, the inner surface of the end cover 23 has recesseswhich are recessed towards the outer surface of the same. These recessesconstitute ball turning grooves 30a', 30a", 30b' and 30b". A detaileddescription will be made hereinunder as to the arrangement of the ballturning grooves 30a', 30a", 30b' and 30b". As shown in FIG. 14, the ballturning grooves 30a', 30a", 30b' and 30b" are disposed on the lines Zwhich intersect the reference lines Y--Y at 60°, the reference line Y--Ythemselves intersecting the line X--X of force acting on the track shaft18 at 30°. The ball turning grooves 30a', 30a", 30b' and 30b" extendalong the lines Z over substantial lengths. One ends of the ball turninggrooves 30a', 30a", 30b' and 30b", which may be referred to as startingends, are positioned in alignment with one ends of corresponding loadedgrooves 13 to 16 and 19 to 20 in the bearing races 11 and 12 and in thetrack shaft 18, while the other ends which may be referred to asterminal ends are aligned with the ends of corresponding non-loaded ballgrooves 7 to 10 in the main body 1 of the bearing.

Namely, the ball turning grooves 30a', 30a", 30b' and 30b" arecommunicated at their one ends with the loaded ball grooves 13 to 16 and19 to 22 and, at their other ends, with the non-loaded ball grooves 7 to10. Thus, one ends of the loaded ball passages constituted bycorresponding loaded ball grooves 13 to 16 and 19 to 20 are connected,through the ball turning grooves, to adjacent ends of correspondingnon-loaded ball passages constituted by the non-loaded ball grooves 7 to10. The other ends of the loaded ball passages are connected to adjacentends of the non-loaded ball passages through ball turning grooves formedin the other end cover 24 which has an identical construction to the endcover 23. Thus, an endless ball recirculating passage is formed by, forexample, the loaded ball passage constituted by the loaded ball grooves13,19, non-loaded ball passage provided by the non-loaded ball groove 7,and corresponding ball turning grooves formed in both end covers (seeFIG. 2).

Semicircular race holding grooves 31 and 32 are formed in the innersurface of the end cover 23. These race holding grooves 31 and 32 havetheir centers located on the reference lines Y--Y which intersect theline X--X of force acting on the track shaft 18 at 30°, and extend inthe recircumferential direction across the ball turning grooves 30a',30a" and 30b', 30b", respectively. Reference numerals 33 and 34 denoteretaining grooves formed in the inner surface of the end cover 23. Eachretaining groove has a substantially hat-shaped cross-section in theplane perpendicular to the axis of the track shaft 18. The retaininggroove 33 has flank portions which extend across the starting ends ofthe ball turning grooves 30a', 30a". Similarly, the flank portions ofthe retaining groove 34 extend across the starting ends of the ballturning grooves 30b' and 30b". The other end cover 24 also is providedwith the race holding grooves 31,32 and the retaining grooves 33,34formed in the inner surface thereof.

Referring again to FIG. 2, a pair of retainers 35 and 36 for guiding therolling of the loaded balls B₁ are provided on the inner surfaces of theskirt portions 26 and 27 of the main body 1. As will be seen from FIGS.20 and 21, the retainers 35 and 36 are formed of steel sheets which arebent to provide hat-shaped sectional shape. The retainers 35 and 36 areprovided at their flanks with slits 35a and 36a which are sized so asnot to permit the balls to pass therethrough and with tongues 35b,35band 36b,36b at both ends of the slit 35a and 36a, respectively. Thesetongues 35b and 36b serve to scoop the balls coming out of correspondingloaded ball passages constituted by the loaded ball grooves 13 to 16 and19 to 22 and to direct the balls to the associated ball turning grooves30a', 30a", 30b' and 30b", thereby to ensure the smooth transfer of theballs from the straight loaded ball passages to the curved ball turninggrooves.

The retainers 35 and 36 are fixed to both end covers 23 and 24 by beingretained at their both ends by the retaining grooves 33,34 in respectiveend covers 23 and 24. As stated above, the tongues 35b and 36b of theretainers 35 and 36 play an important role of guiding the balls duringtransfer from the straight loaded ball passages to the curved ballturning grooves and, hence, are required to have substantial strengthand stiffness. From this point of view, the retainers 35 and 36 arepreferably stiffened by a heat treatment such as tufftride treatment.

In assembling, the retainers 35 and 36 are inserted into the main body 1of the bearing and are retained at their both ends by the retaininggrooves 33 and 34 in the end covers 23 and 24. In this state, thecentral axes of the slits 35a, 36a are located on the same lines as thecenters of the corresponding loaded ball grooves 13 to 16 and 19 to 22.

The operation of the described embodiment of the linear slide bearing isas follows.

The linear slide bearing as a unit is mounted on a track shaft 18 of,for example, machining center (not shown) and a machine is mounted onthe main body 1 of the bearing. As the linear slide bearing as a unit ismoved forwardly or rearwardly along the track shaft 18, the loaded ballsB₁, which are clamped between the loaded ball grooves 13 to 16 in thebearing races 11 and 12 and the loaded ball grooves 19 to 22 in thetrack shaft 18, run in one direction while being guided by the retainers35 and 36. Then, the loaded balls B are scooped by the tongues 35b,36bon one ends of the retainers 35 and 36 and are introduced by thesetongues into the ball turning grooves 30a', 30a", 30b' and 30b" in theend cover 24. Thus, the balls B₁ are transferred from the straightportion of the endless recirculating passage to the recircular portionof the same. The balls coming out of the ball turning grooves 30a', 30a", 30b' and 30b" are then introduced into the non-loaded ball grooves 7to 10 in the main body 1 of the bearing, and run through the non-loadedball grooves as the non-loaded balls B₂. The balls then come into theball turning grooves 30a', 30a", 30b' and 30b" in the other end cover 23and, after making a turn along these grooves, run again into the loadedball passages formed between the loaded ball grooves 13 to 16 in thebearing races 11 and 12 and the loaded ball grooves 19 to 22 in thetrack shaft 18 to run along these loaded ball passages as the loadedballs B₁. The balls are recirculated in rows continuously along theendless ball passages as described, as the linear slide bearing as aunit is moved forwardly or backwardly along the track shaft.

FIG. 22 shows a second embodiment of linear slide bearing in accordancewith the invention. In this Figure, the same reference numerals are usedto denote the same parts or members as those used in FIGS. 1 through 21.

This embodiment is distinguished from the first embodiment only by thearrangement of ball grooves. Namely, in this second embodiment, assuminga reference line Y--Y coinciding with the line X--X of force acting onthe track shaft 18, the non-loaded ball grooves 7 to 10 formed in themain body 1 of the bearing and the loaded ball grooves 13 to 16 and 19to 22 formed in the bearing races 11 and 12 and in the track shaft 18,respectively, are disposed on lines Z which intersect the reference lineY--Y at 60°. No detailed explanation of other portions will be neededbecause the other portions are materially indentical to those of thefirst embodiment.

FIG. 23 shows still another embodiment of the linear slide bearing inaccordance with the invention. In this embodiment, the passages fornon-loaded balls are constituted by non-loaded ball bores 7' to 10'which are formed in the main body 1 by drilling so as to extend in thelongitudinal direction of the main body 1. In this embodiment,therefore, the advantage brought about by the non-loaded ball grooves 7to 10 in the first and second embodiments cannot be obtained, but theadvantages produced by the use of bearing races separate from the mainbody are still obtainable in this third embodiment. It will be clear tothose skilled in the art that this embodiment falls within the scope ofthe invention.

As will be understood from the foregoing description, the linear slidebearing of the invention offers the following advantages.

It is to be noted that, since the bearing races with loaded ball groovesare formed as separate members from the main body of the linear slidebearing, it is possible to effect the grinding and hardening treatmentsuch as quench-hardening of the ball rolling surfaces of the loaded ballgrooves and to enhance the precision of grinding and effect of thehardening treatment thereby to ensure smooth recirculation of balls fora longer period of time.

It is to be noted also that the bearing races made of arcuate membershaving semi-circlar cross-section exhibits a greater resistance totwisting force even under a heavy load so that the contact pressurebetween the balls and the loaded ball grooves is maintained constantalong the length of the loaded ball grooves. This also contributes tothe smooth recirculation of the balls.

In addition, since the bearing races can be correctly positioned andfixed simply by being retained at their both ends by the retaininggrooves in the end covers, the mounting of the bearing races is verymuch facilitated and the troublesome works required by conventionallinear slide bearing such as delicate adjustment of tightening force offixing screws for precisely locating the bearing races can beeliminated.

Furthermore, since the non-loaded ball grooves can be formed by grindingwhich is much easier to conduct than drilling required by theconventional linear slide bearing. Therefore, the non-loaded ballgrooves can be formed at higher precision and in a short period of time,so that the cost of production of the linear slide bearing can bereduced advantageously.

Although the invention has been described through specific terms, it isto be noted here that the described embodiment is not exclusive andvarious changes and modifications may be imparted thereto withoutdeparting from the scope of the invention which is limited solely by theappended claims.

What is claimed is:
 1. A linear slide bearing comprising:an integralmain body with a channel-like cross-section constituted by left andright skirt portions and a central cavity formed between said skirtportions, said main body having a pair of race receiving grooves formedin the opposing surfaces of said skirt portions confronting said centralcavity and non-loaded ball grooves disposed near both ends of respectiverace-receiving grooves and communicating with said race-receivinggrooves; a pair of bearing races constituted by arcuate members having asemi-circular cross-section, each of said bearing races being providedin its inner surface with a pair of loaded ball grooves; a track shaftreceived in said central cavity of said main body and provided at itsboth shoulder portions with ribs extending along the length thereof,said track shaft being provided at the upper and lower sides of each ribwith loaded ball grooves corresponding to said loaded ball grooves inthe adjacent bearing race; a pair of end covers adapted to be attachedto both longitudinal ends of said main body so as to straddle said trackshaft, each of said end cover being provided in its inner surface withball turning grooves for connecting said loaded ball grooves in saidbearing races and in said track shaft to corresponding non-loaded ballgrooves in said main body, and race retaining grooves for retainingadjacent ends of said bearing races; and balls adapted to berecirculated through endless ball passages constituted by loaded ballpassages formed by said loaded ball grooves in said bearing races andsaid track shaft, non-loaded ball passages presented by said non-loadedball grooves in said main body and said ball turning grooves formed inrespective end covers.
 2. A linear slide bearing according to claim 1,wherein, at each side of the longtudinal axis of said main body, one ofsaid non-loaded ball grooves and said loaded ball grooves associatedtherewith are arranged in symmetry with the other of said non-loadedball grooves and the loaded ball grooves associated therewith, withrespect to a reference line which intersects the line of force acting onsaid track shaft at an angle of 30°.
 3. A linear slide bearing accordingto claim 1, characterized by further comprising a pair of retainers,each of said retainers being disposed between said bearing race and saidtrack shaft at each side of said main body and adapted to be retained atits both ends by the inner surfaces of said end covers, each retainerhaving slits corresponding to the loaded ball grooves in the associatedbearing race and in said track shaft.
 4. A linear slide bearingaccording to claim 3, wherein said retainer is provided with tongues atboth ends of said slits.
 5. A linear slide bearing according to any oneof claims 1 to 4, wherein said main body is made of a light-weightsynthetic resin.
 6. A linear slide bearing according to any one ofclaims 1 to 4, wherein the angle of contact between each ball and saidloaded ball grooves in said bearing race and in said track shaft isselected to be about 45°.
 7. A linear slide bearing according to any oneof claims 1 to 4, wherein each of said loaded ball grooves formed insaid bearing races and said track shaft has a cross-section which is apart of a circle.
 8. A linear slide bearing comprising:an integral mainbody with a channel-like cross-section constituted by left and rightskirt portions and a central cavity formed between said skirt portions,said main body having a pair of race receiving grooves formed in theopposing surfaces of said skirt portions confronting said central cavityand non-loaded ball grooves disposed near both ends of respectiverace-receiving grooves and communicating with said race-receivinggrooves; a pair of bearing races constituted by arcuate members having asemi-circular cross-section, each of said bearing races being providedin its inner surface with a pair of loaded ball grooves; a track shaftreceived in said central cavity of said main body and provided at itsboth shoulder portions with ribs extending along the length thereof,said track shaft being provided at the upper and lower sides of each ribwith loaded ball grooves corresponding to said loaded ball grooves inthe adjacent bearing race; a pair of end covers adapted to be attachedto both longitudinal ends of said main body so as to straddle said trackshaft, each of said end cover being provided in its inner surface withball turning grooves for connecting said loaded ball grooves in saidbearing races and in said track shaft to corresponding non-loaded ballgrooves in said main body, and race retaining grooves for retainingadjacent ends of said bearing races; and balls adapted to berecirculated through endless ball passages constituted by loaded ballpassages formed by said loaded ball grooves in said bearing races andsaid track shaft, non-loaded ball passages presented by said non-loadedball grooves in said main body and said ball turning grooves formed inrespective end covers; wherein, at each side of said main body, one ofsaid non-loaded ball grooves and the loaded ball grooves associatedtherewith are arranged in symmetry with the other of said non-loadedball grooves and the loaded ball grooves associated therewith, withrespect to a reference line which coincides with the line of forceacting on said track shaft.
 9. A linear slide bearing according to claim8, characterized by further comprising a pair of retainers, each of saidretainers being disposed between said bearing race and said track shaftat each side of said main body and adapted to be retained at its bothends by the inner surfaces of said end covers, each retainer havingslits corresponding to the loaded ball grooves in the associated bearingrace and in said track shaft.
 10. A linear slide bearing according toclaim 9, wherein said retainer is provided with tongues at both ends ofsaid slits.
 11. A linear slide bearing according to any one of claims 8to 10, wherein said main body is made of a light-weight synthetic resin.12. A linear slide bearing according to any one of claims 8 to 10,wherein the angle of contact between each ball and said loaded ballgrooves in said bearing race and in said track shaft is selected to beabout 45°.
 13. A linear slide bearing according to any one of claims 8to 10, wherein each of said loaded ball grooves formed in said bearingraces and said track shaft has a cross-section which is a part of acircle.